This application is based on patent application Hei.11-153472 filed in Japan, the contents of which are hereby incorporated by references.
1. Field of the Invention
This invention relates to an actuator, such as a truss type actuator for generating an elliptic movement of a driven object by composition of displacements of a plurality of displacing devices where one displacing device is vibrated by vibrations of another displacing device.
2. Description of the Related Art
A first conventional truss type actuator is shown in xe2x80x9cDevelopment of a Small Actuator with Three Degrees of Rotational Freedom (1st Report)xe2x80x9d by K. SASAE et. al., Journal of Precision Engineering Institution, Vol.61, No.3, 1995. In the first conventional truss type actuator, a chip member is provided at a crossing point of three lamination type piezoelectric devices. The piezoelectric devices are driven for moving the chip member so as to trail a spherical surface, so that a spherical driven member can be revolved in an optional direction. Since the piezoelectric devices are driven in non-resonance mode, the displacement of the piezoelectric devices are not so large and the driving efficiency of the actuator is relatively low.
A second conventional truss type actuator is shown in xe2x80x9cManufacture and Estimation of Thin Ultrasonic Linear Motorxe2x80x9d by S. NAGATOME, et. al., Collection of Lecture of Precision Engineering Institution, in Spring, 1998. In the second conventional truss type actuator, a steel plate is blanked so that two displacing portions cross at right angle. Piezoelectric devices are fixed on respective displacing portions. One of the piezoelectric device is resonantly driven for colliding the peak at the crossing point of the displacing portions with a driven member obliquely. Thus, the driven member is moved in a predetermined direction. Since the piezoelectric device is driven in resonance mode, the displacement of the piezoelectric device can be made larger. The peak of the steel plate, however, collides with the driven member linearly, so that acoustic noise and vibrations of the actuator are relatively larger. Furthermore, the steel plate and the driven member are heavily worn. Still furthermore, the actuator has no mechanism for detecting the displacement of the piezoelectric device, so that it is difficult to control the moving speed of the driven member.
An object of this invention is to provide an actuator having a simple configuration and high driving efficiency, and easily be controlled.
An actuator in accordance with an aspect of this invention comprises a base member, a first displacing device held on the base member and displacing by supplying of electric power, a second displacing device held on the base member and displaceable, a compound member for compounding displacements of the first and second displacing devices and a driver for supplying electric power to the first displacing member in a manner so that the compound member moves along an elliptic or a circular trail.
The elliptic or the circular trail of the compound member is conventionally obtained by driving the first and second displacing devices, and the conventional driver has two ways of driving systems for driving the first and second displacing devices. However, the configuration of the above-mentioned actuator can realize the elliptic or the circular trail of the compound member by driving only one displacing device. Since the driver needs only one driving system, the circuit of the driver cam be simplified and the electric power consumption of the actuator can be reduced.